APA (7th ed.) Citation

Norris, R. E. (1995). Gymnocalycium, A Collector's Guide by John Pilbeam. Zenodo.

Chicago Style (17th ed.) Citation

Norris, Richard E. Gymnocalycium, A Collector's Guide by John Pilbeam. Zenodo, 1995.

MLA (9th ed.) Citation

Norris, Richard E. Gymnocalycium, A Collector's Guide by John Pilbeam. Zenodo, 1995.

Warning: These citations may not always be 100% accurate.